Wireless transmission systems may use transmit diversity, in which signals are transmitted to a receiver using a plurality of transmit antennas. A receiving communication device extracts the information from the transmitted signals. Multiple antenna elements may enhance spectral efficiency and capacity, allowing for more users to be simultaneously served over a given frequency band, while reducing signal degradation caused by multi-path and fading. Transmit diversity parameters may be applied to signals transmitted from two or more antennas, and may modify an effective power distribution detected by receivers, such as base stations. The transmitted signals may propagate along different paths and may reach the receiving communication device with different phases that may destructively interfere. The received signal quality may change at a receiver that may be attempting to detect a transmission from a mobile terminal, as well as a noise level created by a wireless terminal transmission in base stations attempting to detect signals from other wireless terminals. A signal-to-noise ratio perceived by base stations may change with varying parameters of transmit diversity control. There is a need for a system, method, and apparatus to reduce interference of transmitted signals.
U.S. Patent Publication No. 2003/0002594, entitled “Communication device with smart antenna using a quality-indication signal,” published Jan. 2, 2003 and assigned to the assignee of the present application, the contents of which are incorporated herein by reference, describes using a power control signal, for example, as provided by the power control bit of the CDMA protocol, as a quality indication signal.
U.S. Pat. No. 5,999,826 (Whinnett) describes a method for remote receiver determination of weights of a transmit diversity array by the receiver being capable of identifying which received signal was transmitted from which antenna. This method requires transmitting a difference reference signal from each antenna. The reference signals are either tones, characterized by different carrier frequencies, different modulating frequencies (tones) or different digital codes. This method requires that the transmission of reference signals be defined by the air interface.